#help-28
1 messages · Page 241 of 1
This is the question I’m trying to solve if ur curious
My notes are on the left, that I’m trying to use, and my working out on the question is on the right
why did your P(Y = y) suddenly all become 1/3
Im trying to do what my notes r on the left
Fir finding the mean
If its wrong mb idk what im doing
ok but in your problem the probabilities are the ones you worked out above
then you just multiply and add them
doesnt matter if it has a 0
just do it
The ones in orange?
yes
Ok give me a bit
Wdym multiply and add them?
as the formula states
xP(X = x)
Like this?
yea
Did I get it right
you missed 3
also small thing in your scratch work
you are multiplying with fractions
not adding
no need for a common denom
just multiply it with the numerator
What
i dont think P(Y = 2) is 8/12
Indeed
Am I meant to use this
You've correctly calculated the orange values but then why didn't you use them properly? @topaz saddle
Huh? This is correct, though, yes
shioshi said 8/12 isnt right tho
????
Why did 2 and 3 become 2/36 and 3/36???? (green part)
By the way, why aren't you using the ORANGE values in the E(y) calculation?
Ok mb I’m tired
Also the correct notation is E(Y), not E(y)
good.
also i make 2/36 so it can have the same denominator no?
so i multiply the top
like i said before
That's not at all how multiplication of fractions work ...
same denominator is only required when you are ADDING/SUBTRACTING
multiplying is not
just multiply with the top of the numerator
done deal
Definitely need to revise BASIC FRACTIONS ALGEBRA @topaz saddle
sorry for caps just wanted to emphasize that
That's only good for you, when we forget something it is obvious that there's a need to revise the topic 🤷♂️ this is how you can get better
@topaz saddle Has your question been resolved?
Closed by @topaz saddle
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
Can someone help me with this?
Closed by @cold wren
Use .reopen if this was a mistake.
👀
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
help on Cii pls
struggling to figure out how to parameterise the surface
so I can dot the curl with the unit norma vector
i have calculated the curl of V but i am not sure how to find the unit normal vector since i would need to do the partials of my parameterisation with respect to their variables crossed producted
<@&286206848099549185>
chatttttt
helppp me por favorrr
@slender finch Has your question been resolved?
@slender finch Has your question been resolved?
@slender finch Has your question been resolved?
@floral scroll
@slender finch Has your question been resolved?
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
how do i do $\int cos^4(x)dx$?
Kiyotaka
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
many ways to go about it
compound angle formula (indefinite)
walli's formula (definite)
@twin willow Has your question been resolved?
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
I need help integrating this expression with respect to x:
im just confused because i see dx in the denominator, so i am thinking of doing ln(x), but since they are derivatives, im not sure i can do that
like I think the answer is da * ln(x) / dy
d²a/dxdy would make sense to me, but this looks broken as given
What's the context?
so honestly, i am doing an astrophysics problem. I am not even sure if i am on the right path for the astrophysics problem, but I have this equation (I solved for Iv), and I want to integrate with respect to omega.
But since this is kind of overcomplicating things, I just thought it would be easier to try and integrate the original problem.
Oh god it's physics notation
sorry, i was trying to keep it math related since ik it's a math server
wait is d²a/dxdy the answer?
Haha that's fair. I wish I knew some astrophysics
no
No I believe Kaynex meant that if the expression was d^2 a / (dx dy) then it would make more sense
i would say da/dy +C(y)
if you differentiate this with respect to x , it gives d^2 a/dxdy because C(y)=0 , it only depends about y
@hollow moth Has your question been resolved?
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
Hi
╰ 𝕃 𝕌 ℂ 𝕀 𝔽 𝔼 ℝ ╮
That 3 is just the size of the mass
No, its 3 mass units
I only know the length of the base
which is 4a
And the length of the base of the right angle if I cut it in half is 2a
Here is a solution to a similar question in the textbook
It just assumes that the the altitude from the right angle to hte hypotenuse is 2a?
I don't understand why
Is there something about equilateral triangles that I'm missing here
isoceles*
U have position of A and B, and u need to find out position of C
Let M in middle of AB
So | (Xb - Xa)/2 , (Yb - Ya)/2 |is position of M
Then calcul Distance CM
@winged elm
@winged elm Has your question been resolved?
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
Anybody know what type of math this is and how i can learn to do it
Get any high school textbook. It's basic geometry.
Or youtube
I just need a name
when i search up line
it doesnt pop up and all i see is lines
What grade u in
9
Get ur 9th grade math textbook
Closed by @clear loom
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
I have the equation v * (dλ/dv). If λ = c/v, does that mean (dλ/dv) = -c/v^2? So then the equation becomes v * (-c/v^2)?
did i do that correctly?
v * d lambda/dv isn’t an equation
wait im confused. is the operator dλ/dv what makes it invalid?
$v \dv{\lambda}{v}$ is not an equation
sorry it's been a while since ive done calculus
knief
and that’s not an operator
Could anyone help me with this one
so to make it an equation, do I need to have another equation and an '=' sign?
basically set 2 equations equal to each other?
Someone else is already using this help channel. If you need help with a question, please open your own help channel/thread (see #❓how-to-get-help for instructions).
or am i lost entirely
not another equation, you have no equation at all
you need an = sign
did you mean
$v = \dv{\lambda}{v}$
knief
okay i think i understand. So I need an equation for dλ/dv. Then once i have an equation (such as v = dλ/dv), do i then cross multiply and take the derivatives respectively?
the original problem is that I need to prove v * f_v = λf_λ.
In lecture, we talked about how f_v = (dλ/dv) * F_λ.
So I am starting with vf_v = v*(dλ/dv) F_λ
sorry the formatting got messed up because of discord. the term is f_λ, not f*λ
$v f_v = \lambda f_{\lambda}$
knief
this?
i'm not sure i was ever given formulas for them. I kinda just assumed i was supposed to use that hint we discussed in lecture. Is it not enough information? Cuz then i'll just do the problem at office hours
is there more context?
can you explain what they are though?
it’s notation for something
what is it notation for
They're both measurements for the specific flux. They just use different units
i’m not physics savvy, are they functions or constants?
do you have the original problem by chance?
astrophysics
im sorry if im taking up so much of your time, i thought this problem was from my lack of calculus understanding, but if it has more to do with astrophyiscs, ill do it at office hours
i think i found your question
thank you so much. Sorry i took so much time of ur time, i just thought it was because of my lack of calculus understanding.
yea i don’t have the physics knowledge to even understand the question
.close
Closed by @hollow moth
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
,rccw
Do you know the vertex of |x|
,tex .abs def
riemann
Plot that and see if you can find the vertex
Emmmmm
Huh
?
Plug 0?
What’s the method of finding vertex, is to find the domain?
@gritty rose 😭helppp
the vertex of |x| is at the origin
3
gg
@tropic lion Has your question been resolved?
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
YOLO need help solving this rhombus
Yes
Ye
Recall that the diagonals of a rhombus are angle bisectors
For example, DB bisects angle ADC
Yes
So think of how you can work backwards to get ADE
Oh yeah the diagram resets after each problem
Will it still be 27
What does the angle bisector tell you about angle ADE
Idk
ADC
How would I find adc??
- what are you given
- how does it relate to ADC
You should notice that they’re adjacent angles
Take that as you will
Further hint: ||think of your angle relationships from parallel lines||
Ahhh
Sooo supplementary???
OHHH
ADC equals 80
YEAH???
And the half of that is 40
How is ADC = 80
How is 180-140=60
40?
Yeah ._.
@late flame Has your question been resolved?
.close
Closed by @late flame
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
I dont understand why for part a
we multiply the x value by 2
but then in part b
we compress it by 4
how dyu know when it should be compressed or stretched out
yes
@neat terrace Has your question been resolved?
@neat terrace Has your question been resolved?
when u had to sketch graph of f(x) from f(2x) you stretch out
when u have to sketch graph of f(4x) from f(2x) you compress
making f(x) from f(2x) means
f(x) attains values 1/2 the speed of f(2x)
hence stretched
where in 4x its twice the speed of 2x
hence compress
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
I didn't understand the question as well as the logic used for it
Yes
Yes
and since we put the card back in, that never changes
Yes
and we want to look at the probability of getting at least one heart over multiple draws
so for example what would that be if we draw 3 times?
So p(x>=1)
1-27/64?
1 - (3/4)^3, yes
ok
so if we do n draws then what will be our chance of getting at least one heart
Will increase
Right? Cause it'll just be 1-(3/4)^n n= number of cards we have picked and put back?
1 - (3/4)^n, yes
i did say n draws
ok
now your questions are
find the smallest n for which that >= 1/2
and find the smallest n for which that >= 3/4
Ohh
That makes sense
But I still don't get how 'there is atleast an even chance of drawing a heart' makes n>=1/2
"even chance" means one half probability
Ohhhh
it is a somewhat old fashioned wording
And after this what do we do?
after what
So this is incorrect?
Figuring out What the questions mean
For this we need to find n in (3/4)^n=1/2 and next one (3/4)^n=1/4?
it is correct but phrased in a different way and (independently) a bit overcomplicated
<= on both, not =
...
no,
after solving the inequalities, you need to find the smallest natural n which satisfies them
and those smallest n's are your answer
Solve this by using log?
some logarithms will happen yeah
yes
And 2nd one n=5?
Btw
How do you understand these questions
Like what's your train of thought
For probability questions permutations and combinations those types of stuff
@solemn sand Has your question been resolved?
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
Can anyone verify if this is correct?
If you keep following the predecessor it has to contain the 0 vertex at some point right?
@wheat swallow Has your question been resolved?
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
im not sure how to start
What does u.v=0 imply?
first understand what the problem gave u
same thing
that u and v are perpendicular if their dot product is 0
sorry we didnt learn what span is yet
Alright
Say you have (0,1) and (1,0) column vectors
Can you express any vector w = (a,b) in terms of them in R²?
Yes
we can use linear combination?
Yep
Yes and e1=u and e2=v because both u and v will "generate" R² like (0,1) and (1,0) do
For example just consider u=(0,1) and v=(1,0)
so how can we use this to help us?
so w=xu + yv
proj_u(w)=?
Take w=(1,1)
w = 1(1,0) + 1(0,1)
proj_(1,0)(w) = ? (the projection vector you get after projecting w onto (1,0))
,rccw
this what i have so far
Indeed. Try to simplify it a bit using u.v=0
Sure np
the handwriting is so ass beam 💔🥀
stfu
okay im back srry was helping a friend
im sending image
idk if my i did any illegal algebra so llmk
All legal
great
So it's xu
am i allowed to cancel u dot u on top and bottom
Yes because they're scalars
oh right
Similarly, proj_v(w) = yv
yea
With this information at hand, what options can you eliminate from here?
i think option a is not always true
this info is not needed nvm
yes
So what's (xu).(yv) ?
Yep
so then option A is true
Indeed
option B is going to be w = xu + yv
isnt that just linear combination thats what we said was true right
Indeed
To see why you need to prove that u,v will "generate" (or span) the entire R² when u.v = 0 (equivalently you can express any vector in R² in terms of u,v)
You'll hopefully see this when you'll do span
ah okay
so option C is saying that xu + yv = xu OR xu + yv = yv
i cant see how that will be true
Yep not always true
Indeed
ohhh ok i get it now thank you 🙏
Np. Have a great day
Closed by @twin wolf
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
I'm not sure how to start (12(a))
@waxen cliff Has your question been resolved?
.close
Closed by @waxen cliff
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
hi guys so i was trying to solve a quadratic function with Bhaskara's formula.
the function is
The quadratic?
Bhaskara's formula? & what are you actually solving? the equation f(x)=0?
bhaskaras formula is just quadratic formula iirc
its another name for the quadratic formula
brazilian acc to a google search
and so i put the coordinates on desmond to keep better track of how it was coming togheter
3 does not work
You did something incorrect
your substitution might be incorrect
i dont think your roots are right tho
yeah can you show your working for this
like how exactly did you go about and get the coordinates you stated
ok
so first i naturally replaced the values with the corresponding ones of my function (sorry for using paint to do this)
b is -4
-b is 4
oh f god
gimme a moment i need to quickly try that
guys i think i fd up again
Yes, but I divided both sides by -2
Just to clarify, it's -2x^2 - 4x + 6 right
for f(x)
So if f(x)=0, then -2x^2-4x+6=0
If you divide both sides by -2, we get x^2+2x-3=0
I used the divided equation for the formula rather than the original
i think i get most of it but where has the -2 gone?
nvm it became invisible since its a 1 now, rihgt?
I don't think the -2 matters once you've divided both sides by it
And if you use the original, it still wouldn't be a problem
For this, you have (4+8)/-4 or (4-8)/-4
So 12/-4 = -3, -4/-4 = -1, which is identical to the answers I got
your simplification is incorrect
your fractions are correct
i get it now, and it does match the roots that desmos says tysm
No problem
It's okay, it takes time. If it helps, I usually just directly turn it to +4 for the sake of less brackets
Closed by @trim umbra
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
Hey, I'm solving some differential equations using the method of undetermined equations and I stumbled upon a problem where the particular solution is a product of a polynomial and an exponential function, I'm not sure how to get the Particlar solution, help is appreciated.
Do you know how to solve differential equations like these in general?
yes but Ive never solved one where f(x) is a product of a poly and an expo
What method do u follow?
the method of undetermined coeffs
that's what I initially did but I got an unsolvable system for the 3 constants
a, b and c
Interesting
Cause I got a = 1/2, b = -15/16 and c = -5/32
Oh, wait
Nvm
,w 715/162-9/2-4/9
is that c?
That ÷ 7 is c
a = 4/9
b = -143/162
c = -43/567
This is what I got
,w y'' + 2y' - 6y = (8x^2-7x-9)e^(4x)
hmmm
And then there's the constant terms
Which idk how to get
,w 2a + 8b + 16c + 2b + 4c - 6c
Closed by @civic lintel
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
i have a really general question im typing this in my ti84 and i keep getting dimension error could someone help me
im doing matrix a as 4x2 with u and v and then matrix b as 4x1 with w and then doing rref(augment([A],[B])) and keep getting dimension error
.close
Closed by @simple sandal
Use .reopen if this was a mistake.
in the ti-84 RREF can only be done if there are at least as many columns as there are rows (for some reason)
Could you send a picture? Also, did you get your question resolved?
yeah got it resolved
you can get around this by augmenting additional 0 columns
yeah i rmb my prof mentioning this and i just found it in my notes
thanks a ton
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
do you mean rho(2) depends on rho(1) ?
@storm flint Has your question been resolved?
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
Can someone look at my proof and tell me if it’s valid and give feedback if possible, this is a proof for the associative identity using the Peano axioms and the propositions in the Analysis I book by Terence Tao this is my first time trying to do a real analysis proof (I’m technically in high school but self teaching) so bare with me if it’s not the greatest 😭🙏
@urban steeple Has your question been resolved?
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
then after this i dropped a perpendicular from that pt (blue yellow intersect) to the ground
or did i do the first step itself wrong
@sturdy valve Has your question been resolved?
Hi
why do you think light ray is perpendicular to the ground after it crosses the transparent liquid
nono
i didnt say the light ray is perpendicular
i just drew a perpendicular
imaginary line
for calculations with angles
oh i see
you should be able to figure out the angle of incidence at the blue line given refrac index = sqrt(3)
and snell's law
oh and from there i can get refraction angle
i will try
in sometime..i moved on to another question give few mins
@gritty rose im not able to find angle of indicence 😔
incidence
did you try to use snell's law
and did you find the angle the light ray makes with the liquid
@sturdy valve Has your question been resolved?
yes
and why are you stuck
the angle of refraction?
the angles in this right triangle
yeah no i wasnt able to find it
you also need to find this tangent line in terms of the angles as well
then you'll have two equations and two unknowns
oh ok so i should find the angle that makes with the ground?
ykw im done with this question for now
ty for helping
.close
Closed by @sturdy valve
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
"is the orthogonal projection of v on n" what about the orthogonal projection of n on v? I'm confused because the scalar product is meant to be commutative
n on v would just be the case where v is the unit vector instead of n
(yes scalar product is commutative so flipping it will still give you the original projection)
but flipping which one is a unit vector changes the projection
also this is slightly wrong
$( \mathbf{\hat n} \cdot \mathbf{v}) \mathbf{\hat n}$ is the orthogonal projection
rafilou is not not born in 2003
$\mathbf{\hat n} \cdot \mathbf{v}$ is only the coefficient of the orthogonal projection
rafilou is not not born in 2003
sometimes people call the coefficient of the projection the "scalar projection"
@high ridge Has your question been resolved?
Closed due to timeout
Use .reopen if this was a mistake.
Send your question here to claim the channel.
Remember:
• Ask your math question in a clear, concise manner.
• Show your work, and if possible, explain where you are stuck.
• After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!
Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.
the first image is my notes and what ive done so far for this and previous questions, I am not sure if everything is right, nonetheless, I am stuck. I am not sure what my professor means of 'What identity do we have for sin2alpha'
and im stuck on how to rewrite the area of the isoscles triangle in terms of r and theta
if this is confusing lmk, ill do my best to explain again. I am just lost about all of it entirely haha
(have you heard of the double angle formulas? or the addition ones, how to expand something like sin(A + B)? I presume that's what they're after)
the sin(2alpha) = 2sinalpha cosalpha
that?
to be honest no... my previous prof skipped that whole chapter so I have never done them before..
😭
As for rewriting, isn't that just a matter of using theta = 2alpha in the expression for the triangle area you found above it? 
Damn
that's annoying 
yea my professor skipped A LOT so im very frustrayed they said, 'its not that important to know going into calc, just extra stuff'
sooo like writing it as, sin(2alpha)= 2sinalpha cosalpha=sin theta?
wait idk
AH
That's not great
esp when it's likely they'll use things you're assumed to have learned before in multiple areas 
i feel like you use trig identities for like half of calc 2 🙏
bro.. welp guess im going to have to go back and teach myself 😭 😭
(and you can use that as part of it sure, but also as alpha = theta / 2, that should then give you a nice way to find the area of the triangle too
)
in other words, putting alpha = theta/2 here (and then of course you can double angle simplify stuff too!)
im sorry if its too much trouble, but is there a way you could draw what you're saying (if that makes sense) onto the image. Because reading everything rn i feel like my head abouta explode 😅
if it is, you dont gotta <3 i can figure it out LOL
What I was trying to say is that you can say
[
\frac12 (2r\sin(\alpha))(r\cos(\alpha)) = \frac12 \qty(2r\sin(\frac{\theta}2))\qty(r\cos(\frac{\theta}2))
]
(and of course, that right hand side is still simplifiable)
@devout valley
The right hand side is the area for A in terms of only r and theta, though not in its simplest form 
ohhhhh okay okay i see
so then to simplify I would times it by its reciprocal right?
oh wait
wouldnt the 1/2 and the 2 cancel out?
They can, but don't cancel them out for now 
(or part of it
)
OHHH
so with that equation i can divide it by 2 then to simplify it even more????
OMMG 💅 my gears are back online
Or more what I'm hinting at, you can factor both of the $r$'s out of here, then you get
[
\frac12 r^2 {\color{green} \qty(2 \sin(\frac{\theta}2) \cos(\frac{\theta}2)) }
]
@devout valley
It should hopefully be clear what the green turns into, you already got it 
i think i do, because the green was what i typed earlier right?
yeyeye then i do
idk if you lookes at the other guided questions, but the steps you and I did together, does that answer those questions? or are there more to this problem? that im missing
i think so... but i just wanted to make sure
For the ones before, do you have like the full prompt from here? I feel that for example...
...here may not be the answer they're looking for, though you're not "wrong" I would say
I'm personally happy with them, pretending you were doing them for me 
would you like for me to send you the full image?...
Yes please 
Ah I see, I think you're fine in that case
seems like the guiding questions are more like supposed to lead you to answer the "main questions", I think 
yea im starting to think, thats the case to
im sorry if im taking up your time but i had a question for number 5?
You aren't taking my time up, I'm chilling and eating and would be happy to help 
youre awesome
so when it says n is it the number of sides in the polygon?
in this case would it be 8?
Yep, in the pictured one it would be 8, but it can be whatever in general 
You can, and very much should, make use of that, yep 
(look at the picture
I think you know what to do
)
okok, i believe im comfortable enough to do this one of my own...thank you so much for the help ❤️
Awwww, it's always a pleasure to help you
see ya around soon 
.close
Closed by @supple plover
Use .reopen if this was a mistake.
.reopen
✅
ahhh im sorry, i realized something and im now confused
for the equation in what i wrote sin(2alpha)= 2sinalpha cosalpha=sin theta?
would the alpha be theta instead?
oh ok
Gonna interrupt you 
You know both that $2\sin(\alpha)\cos(\alpha) = \sin(2\alpha)$, and also that $\theta = 2\alpha$, which is presumably the way you got there
@devout valley
mhmhm
So then you could of course plug that in 
That's just saying this in a different order
if that helps? 
yeaa so, the equation is 1/2r^2 (2sin alpha(cos alpha))?.....
Yep, that's one form of the equation, then of course as above, you can cook more with that and get something nice, in terms of only r and theta as they asked 
is that when we cancel out of 1/2 and 2?
Not like that 
oh
notice inside the
here, you have...
...the left hand side of this 
OH it simplifyes to the sin(2alpha)
So you can simplify the formula to (1/2)r^2 sin(theta) 
Yep that's it 
how would I answer the 'what part of this identity is present in the equation we have' guided question for #4? I am confused on what they mean by part?
unless im being slow
Basically how you manipulated it 
The green (you can replace the theta/2's with alphas of course)
ohhh i see what u sayin
You can basically say something like "oh look, we have (1/2)r^2 * (2sin(a)cos(a)), but oh shit, that (2sin(a)cos(a)) is in the identity 2sin(a)cos(a) = sin(2a), so we can use that" (of course, a bit more formally worded of course
)
Yep it is 
chart im not even kidding, they want this due tonight and im question 4 out of 10. I am so grateful to you rn for helping haha
Awwwww
that's quite mean though, esp if the questions are this long 
Are the questions the numbered bits here, you mean?
they said it shouldnt take more than hour if you knew what you were doing
yeaa
these are the next of them
Ohhh, I was about to think they were going to set you like multiple of the whole set of questions, I'd have died if it were like that 
LMAO OH
And well, we definitely will get them done by the end of the day at least (assuming you have the time) 
yup I do! I canceled plans to get this done and im PST so I have a bit before its 11:59
Awww
yea you'll be alright then 
We can walk through as many of these as we can (and I think we can manage them all!)
OMG YOURE AWESOME
so for 5, when they ask in the guided questions how many triangles are there. Are they refering to like the sides?
ima try to draw at what im refering to
oh wait
the pink line
What about it?
(I think you see where you're meant to go!)
okok
[they're basically asking you how many of these you have
]
Pretty much yep, there isn't like a time limit, basically until you're done with the questions 
ohh i see
thank you
for when they ask what the area of the shape is, do they mean an equation or a value? And if its a value wouldn't it just be what n is equal to?
Well, I mean, the area will be an expression that depends on your variables n, r and theta
It won't be just n though, if you think about it for a moment-
You know the area of each of these triangles, we just found it, they have area (1/2)r^2 sin(theta), and you can make that polygon with multiple copies of those triangles
How many triangles do we have?
What if n was 5? 13? 69?
we have 5 triangles, 13 triangles and 69 triangles 😏
so whatever n is, is how many triangles?
Yep
I was trying to get you to say "there are n triangles" 
ohhhhhh
LOL
so then would we implement the n into the equation we just found?
if implement is the right word haha, my brain
I'll let you have that one 
So, now, we have n triangles, each of them having area (1/2)r^2 sin(theta) each, so what's the total area?
It's an easy question 
it is? am i just overthinking it? lOL
You probably are
which is why I said it's easy 
is the answer in this text
It isn't yet, but it's basically one step to get it 
"if I have two cats that love to stalk me, and each of them are 4kg each, what is the total weight of cats I have to carry?" 
Let me change my question a little bit again, what if instead now I had four cats, still 4kg each? 
well it would be 16kg in total for all four cats
The triangles are the cats, the triangle areas are the cat weights
so we have 4 triangles, the triangle areas is the equation we found earlier ( the (1/2) r^2 sin theta)) ?
would we then be essentially adding the triangle area equation thingy mabob together??
Basically yep, by however many triangles you have 
Of course, in the general case, replace 4 with n 
If I had n cats of mass 4kg, then I’d have to carry (4n) kg of cats, who would probably be very amused (and waiting for their snuggles
)
If their mass was instead (1/2)r^2 sin(theta), I think they’d be looking at me as to why they have such a weird mass, and wondering if I’m trying to use them to explain a problem to someone 
LMFAO
reading this problems makes me want to snuggle my cat
anywho
so then would be mulitple the 4 into the (1/2)r^2 sin(theta) equation?
If you can’t tell, I’m missing some of my troublemakers 
OMG how many kitties do you have?
And exactly that
and if it were a general n instead?
we would times the n into the equation?
Well, I don’t actually “have” any cats, but there are a total of 5 that pretty much love to follow and chase me any time I step outside my house 
AWWWWWWWWW
They’re not even mine but they follow me like they think they are, they even like to sit on my lap too 
If I sit down outside then there’s one who’ll just jump up and demand to be petted 
would the equation be n * (1/2) r^2 sin theta?
AWWW
i wish we had cats roaming around like that
There's too many wild animals around, for there to be kitties..
Awwww 
(And yep exactly that
)
You would, but we want it in general for our answer, it’s like our recipe 
i see
This is the answer we wanna give 
ohhh so that equation is the answer
Yep it is!
picasso
Oooh that’s a cool emote I didn’t think I had
hehe
was that also a way to find the answer to number 6?
its super cute
Well, not really, but 6 is easy peasy 
okok well we aint there yet, so we can put a pin in it
We are there
we’ve done the area question already haven’t we? 
Yep, now, time for us to get cooking 
Not that easy, no 
dang..
Anyways, if you excuse my poor drawing 
That’s what we have when n is 8 
mhmhmh
We have n (= 8) copies of those triangles, so how many copies of theta do we have?
8?
Yep, that’s it 
So, with my Excellent™️ drawing skills, we see we have 8theta when we go around the center of the circle, right?
mhmmh i see i see
And so, what must that 8theta work out as?
(I think at this point, I should be doing the guiding questions
)
Well, to an extent, we’ll come back to radians in a moment-
oh okok
Do you know what the angle at the center of a circle must work out as? Either in degrees or radians, whichever unit is fine for now 
for some reason im wanting to say pi, but i dont believe thats right
180 degrees is the line through the circle
which is also pi
WAIT I CAN COOK
nvm you lost me, i cant find anything about it in my unit circle notes..
i dont think its one of the things my prof went over
It’s one of those things that you can’t really hint at without giving away the answer 
is it 0
It is something I know you know, but I don’t know how to ask in a way 
Not quite the answer I’m looking for 
If I spin around once, I’ve made a [what] degree turn?
360
That’s it 
oh wait, DUH OMG
It really is one of those things that’s so easy it’s hard, isn’t it 
yea fr
The 8theta works out as 360 degrees, or 2pi radians
So, as we’re gonna be using radians, as they’re better
we have 8theta = 2pi, right? 
mhmhm, quick question how do we know 8 theta is 2pi and not like 4pi
8theta is the “spinning around once”
If you look at the picture, you see that they all add up to make the “centre” angle of the circle, which of course is 2pi (because you only go around once)
mhm i see, so if it was 4theta it would still = 2pi because they all add up to make the "centre" angle of the circle?
Yep
and same for whatever value of n you have 
YAY okay i understand
Which of course is the general case, n * theta is 2pi 
now we back to this
8theta =2pi
wait is that just the answer for number 6
Waaaiiittt 
Let’s go here 
okkk
Don’t be sorry 
Remember that we want to express n in terms of theta, that was our aim 
mhmhm
So if n * theta = 2pi, then what’s n?
8?
Not quite what I want 
I’m kinda asking you to rearrange this to make n the subject 
like n = blah blah blah instead?
then would we divide?... so its n= 2pi/theta
yippiii
youre awesome
If this is the area that we have, but also…
n is this, can we rewrite the area without an n showing up? 
so then its just r and theta?
We only want to see r’s and thetas, and no n’s 
mmhmhm so we gotta make a replacement somewhere
im assuming
WAIT
could we just replace the n with the equation?
YIPPII
Hehe, told you these aren’t too bad 
yup after figuring out all the others it pieces together
You have to admit that I’m better at the guiding questions then they are, right 
Awwwww 
sadly i have to go back and individually answer the questions as its part of the grade, but thanks to your help itll be a breeze
Awwww, that’s fair enough
I do hope they’ll be fine though, and that you’ll see how to do them, after all, we’d have walked through everything, and we’re so close to done!
YUP!
luckily thanks to this being on text i can go back too if im stuck on something
OKAY question 8 cooking time
Yep you can always refer back to what we’ve done, you can search your messages and find what we did 
Yep yep 
For that, you notice that the more triangles we start to get, the closer the polygon starts to look like the circle, right?
yea i see that
So, the idea is that we wanna take more and more of those sides, making n larger, which then-
Time to make you answer their guided question
as n gets larger, what happens to the angle of each of those triangles, the thetas?
The angles don’t get larger, no 
oh
Think about here, when n = 8
And compare it to, for example, if n = 3 or something
mhmm
Or alternatively, remember you have this here!
For both of them, they’re basically telling you something-
For this one, we can also have theta in terms of n, for which, if n gets larger, what happens to theta?
whatever value it is, its equal to 360 (2pi)?
Thats the total of all the angles taken together 
oh i see
If you had more triangles, you certainly can’t have the angle theta getting bigger, else that would mean you end up getting larger than 2pi, which we don’t want!
yea yea
haha 10/10
Hopefully you notice how the “theta” for the n=4 is bigger than the corresponding one for n = 8, right?
yea i can visually see it
Cool, so, finish the sentence with what you think: “as n gets larger, then theta gets [?]”
idk why im wanting to say smaller, because the triangles are smaller for n = 8
Why do you not know
you’re right 
OH YAYYYYY
The thetas do get smaller, have some more faith in yourself 
yes teach 🙏
Another way to see it too is that theta = 2pi/n, and as n goes to infinity, you basically have a fraction with a larger and larger denominator, making the fraction smaller and smaller, decreasing to zero
If you’re happy with that as well? 
yea that also makes sense, but not as much as the picture
so then with this information we write into an expression?
Pictures are worth a thousand words of course 
very true thats why me likey
Well, more that you say something like “as n -> infinity, then theta -> 0”

